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Analysis

Luau Bytecode Structure & FastCall Opcode Analysis (OP_FASTCALL, OP_CALL) [v2.4 Technical Discussion]

luau_hacker
Luau Expert
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1 maanden geleden ยท Jul 1, 2026 1:08 PM
#1

Deep dive into Luau VM bytecode instruction set:

In Roblox Luau, standard Lua calls are optimized via OP_FASTCALL opcodes which bypass function lookup overhead for built-in library functions (math.sqrt, string.byte, table.insert).

  • OP_FASTCALL1: Unary function call
  • OP_FASTCALL2: Binary function call
  • OP_FASTCALL2K: Fast call with constant operand

Understanding Luau opcode layouts allows writing custom disassemblers and bytecode execution engines!

vtable_slayer
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1 maanden geleden ยท Jul 1, 2026 4:37 PM
#2

Luau's fastcall architecture is a brilliant engineering enhancement over standard PUC Lua 5.1 bytecode.

ghidra_pcode_pro
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1 maanden geleden ยท Jul 2, 2026 5:10 AM
#3

Great breakdown of Luau compiler optimizations.